Secondary storage facilities used in data processing systems generally comprise a storage device controller and one or more drives connected to the controller. The drives include, but are not limited to, direct access memory devices, such as magnetic disk and magnetic bubble memories.
These secondary storage facilities, especially facilities using magnetic disk memory devices as the drives, have become very sophisticated in recent years. However, in efforts to increase performance, interconnections between controllers and drives have increased in complexity. One of the more significant results of such increased complexity is that controllers are adapted to be used only with certain drives, and vice-versa. This is a result largely of the communications employed between a controller and a drive. Thus, as new drives are developed, it is generally necessary also to develop new controllers for use with them.
Cabling and connector costs also have become significant, since high reliability is needed and information must be transmitted at high rates. Such costs, in turn, are directly related to the number of conductors needed in the cable; each conductor requires at least a receiver and/or transmitter for the termination at both the controller and drive ends of the cable.
Further, multiple controllers and/or drives frequently are interconnected via a time-shared communications channel, termed a bus. By nature of the time-sharing arrangement, an individual controller generally can communicate with only one drive at a time.
Therefore, it is an object of this invention to provide a secondary storage facility and, more particularly, an interconnection between controllers and drives in such a facility, wherein the complexity and costs of interconnecting a drive with its controller are reduced over prior secondary storage facilities.
Another object of this invention is to provide a standard interconnection for future block-addressable secondary storage system products, which is not drive specific and, thus, supports an arbitrary mix of controller types and peripheral drive types.
Still another object of this invention is to provide a controller/drive interconnection which is capable of permitting communications between a controller and drive at a high bit rate.
Yet another object of this invention is to provide a secondary storage facility in which the cabling between the controller and drive may be physically small, utilize a minimum number of conductors and be up to at least one hundred feet in length.
Another object of this invention is to provide a wide and flexible architecture in the storage system interconnection, via the use of a hierarchical, multi-level communications protocol.
Still another object of the invention is to provide an interconnection whereby the controller is provided with effective real-time rotational position sensing information concurrently from every drive with which it is connected.